These files represent uncertainty surfaces accompanying the datasets
"Historical built-up areas (BUA) - gridded surfaces for the U.S. from 1810 to 2015"
"Historical built-up property locations (BUPL) - gridded surfaces for the U.S. from 1810 to 2015"
"Historical built-up property records (BUPR) - gridded surfaces for the U.S. from 1810 to 2015",
contained in the dataverse �HISDAC-US: Historical Settlement Data Compilation for the United States� 
(https://dataverse.harvard.edu/dataverse/hisdacus).

Reference:
Uhl, Johannes H.; Leyk, Stefan, 2020, "Uncertainty surfaces accompanying the BUPR, BUPL, and BUA gridded surface series",
https://doi.org/10.7910/DVN/T8H5KF, Harvard Dataverse.

The gridded surface MAX_NUM_MULTIRECORDS.tif represents the maximum number of multi-records found at a multi-record location within each grid cell.
Multi-record locations involving residential income, or office / residential condominium related land use types are excluded.
This surface allows for quantifying the locational uncertainty associated with the BUPR, BUPL, and BUA surfaces.
Large values indicate potentially higher levels of uncertainties in the geolocation of the records used to generate 
the BUPR, BUPL, and BUA surfaces.
Extremly large values may represent pseudo-locations that may be refined in future data / database versions.
Data users are encouraged to exclude BUPR grid cells with extreme values in MAX_NUM_MULTIRECORDS if density-based analyses 
are conducted based on the BUPR surface series. 

Abbreviations and explanations:
BUA:			Built-up areas. Grid cells containing at least one built-up property in a given year.
BUPR:			Built-up property records. Individual built-up property records in ZTRAX, representing a building or building unit, depending on ownership situation.
BUPL:			Built-up property locations. Unique locations of built-up property records (i.e., buildings or building units), independent from ownership situation.
Multi-record: 		Multiple built-up property records sharing the same geospatial location.
Multi-record location: 	Geospatial location at which multiple built-up property records are referenced to.

Data source: Zillow Transaction and Assessment Dataset (ZTRAX) (c) Zillow Inc.
Spatial resolution: 250m
Coordinate reference system:
USA Contiguous Albers Equal Area Conic USGS version (SR-ORG:7480)
https://spatialreference.org/ref/sr-org/usa_contiguous_albers_equal_area_conic_usgs_version-2/
Proj4: +proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23.0 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +datum=NAD83 +units=m +no_defs

Contact:
Stefan Leyk
Department of Geography
University of Colorado Boulder
GUGG 110, 260 UCB 
Boulder, CO 80309-0260, United States of America
stefan.leyk@colorado.edu